1. Field of the Invention
This invention relates to hydraulic dampers of the cylinder and piston type used for controlling the fore and aft movement of helicopter rotor blades in their plane of rotation. More particularly, this invention relates to means for providing redundant seals, a fluid reservoir, and a means for accurately indicating when the seals for the damper have become worn and are leaking excessively; all in a closely contained system.
2. Description of the Prior Art
Dual seals have been used on the shafts of dampers and servomotors and the like with fluid pressure indicators connected to the area between seals to indicate leakage past the primary seal. U.S. Pat. No. 1,943,578, issued January 16, 1934 to G. E. Bigelow et al shows such an arrangement applied to a high pressure centrifugal pump shaft. The area between the seals is connected by a conduit containing a restriction (valve) to a low pressure system and a pressure gage is connected to the conduit between the restriction and the seals. This arrangement proved objectionable because a pressure built up in the return line for the leakage fluid, thereby giving a false indication of leakage. In addition, this arrangement requires the use of external fluid lines, a separate reservoir and a pump to collect the fluie leakage and return it to the high pressure system. This arrangement is not optimally suited to a helicopter rotor application as the added complexity would hamper performance and limit reliability as well as increase cost and weight.